The present invention relates to a novel epoxysuccinyl amino acid derivative of the formula ##STR2## wherein R.sup.1 is hydrogen, alkali metal, benzyl or cycloalkyl having 5 to 6 carbon atoms, R.sup.2 is alkyl having 3 to 4 carbon atoms, R.sup.3 is hydrogen, benzyloxycarbonyl, acetyl or benzoyl, and n is an integer of 2 to 7.
The prior art discloses E-64, ie., N-[N-(L-3-trans-carboxyoxirane-2-carbonyl)-L-leucyl]agmatine (U.S. Pat. No. 3,911,111), its intermediates [Chemical Abstracts, 87, 202108y (1977), ibid., 87, 85238c (1977), ibid., 87, 202125b (1977), ibid., 87, 68128z (1977)], and epoxysuccinic acid derivatives of German Patent Laid Open Application No. P 28 09 036 and Chemical Abstracts, 87, 681239a (1977) prepared by several of the present inventors.
The compounds of the present invention are distinguished from the prior art compounds by inhibitory activity to thiol protease, especially, calcium-activated neutral thiol protease (hereinafter referred to as CANP) which exists in excess in muscle tissues of mammals afflicted with muscular dystrophy, and by good absorption and distribution in tissues after administration to such mammals without acceleration of vascular permeability.